Process of baling switchgrass into rectangular high density bales optimized for highway transport on semi-trailer trucks to biorefineries

ABSTRACT

Process of baling a switchgrass biomass material at between about 22 and about 32 psi into a rectangular switchgrass bale having a bale density of between 14.6 and 20.5 lb/ft 3 . A 3×4×8 ft switchgrass bale so produced weighs between 1,402 and 1,968 pounds.

STATEMENT OF GOVERNMENT LICENSE RIGHTS

This invention was made with government support by the NIFA SmallBusiness Innovation Research program of the U.S. Department ofAgriculture, grant numbers 2005-33610-15483 and 2006-33610-17595. Thegovernment has certain rights in the invention.

FIELD OF THE INVENTION

Our invention relates to harvesters, particularly balers, and provides abaling system engineered to produce rectangular bales of tall grassbiomass, using a preselected platen pressure to achieve a predeterminedbale density, taking into consideration initial moisture content,expected dry-down period, and mode of transportation.

BACKGROUND OF THE INVENTION

The terms “tall grass” and “tall grasses” as used herein refer toswitchgrass (Panicum viratum), miscanthus (particularlyMiscanthus×giganteus), big bluestem (Andropogon gerardii), Indian grass(Sorgastrum nutans), reed canary grass (Phalaris arundinacea), and othertall perennial grasses harvested as biomass feedstocks for ethanolproduction and biorefining.

Tall grass biomass is expected to become a core element of our nation'sstrategy to replace imported oil and natural gas with renewableresources.

Currently, switchgrass is harvested in large rectangular bales (3×4×8feet) weighing about 1,100 pounds (11.5 lb/ft³) at about 10 percentmoisture (Austin, 2009). For example, a New Holland BB9080 large squarebaler intended for forage and straw crops reportedly producedswitchgrass bales at an average bale density of 181.1 kg/m³ (11.3lb/ft³) at 80% of the baler's plunger load setting; this baler was saidto have the ability to produce switchgrass bales that approach 200 kg/m³(12.5 lb/ft³) (Kemmerer and Liu, 2010).

The present inventors have reported their progress to develop bettermethods to collect and transport woody biomass (Dooley 2006; Lanning2007; Dooley 2008; Dooley 2009). Our continuing goal is to engineer moreefficient recovery and highway transport of plant biomass materials tosecond-generation bioenergy and biofuel plants.

SUMMARY OF THE INVENTION

We have elucidated the three rheological properties of tall grassbiomass material requisite to predictably and reproducibly bale tallgrass biomass at preselected optimum highway transportation densitieswhile minimizing fossil fuel consumption during baling, handling, andtransport.

First, we have empirically determined the baled bulk density (lb/ft³) v.platen pressure (psi) curves for tall grass biomass at various moisturecontents. These relationships indicate the target compression platenpressures that will compress tall grass biomass, e.g. whole stalks orbillets, to predetermined transport densities.

Second, we have empirically determined that tall grass biomass materialcompressed to optimum transport densities has a Poisson's ratio effectof about 22%. This value is required to determine the minimum mechanicalstrength of baling chamber sidewalls, be they fixed or moveable, forproducing tall grass biomass bales of optimum transport densities.

Third, we have observed that tall grass biomass material compressed tooptimum transport densities has a coefficient of friction against steelbaling chamber walls of approximately 0.40. This value is necessary, inconjunction with both the target compression platen force and thePoisson's ratio value, to determine the minimum platen pressure requiredto form and eject a compacted bale of tall grass biomass from the balingchamber.

These three discoveries permit one of ordinary skill to for the firsttime calculate the requisite strength of tall grass biomass compressionsystems and baling chambers, which in turn permits one to manufacturerobust, lightweight and economical rectangular balers to produce tallgrass biomass bales at high densities optimized for transport onconventional semi-trailer trucks.

Accordingly, the invention provides a biomass baler having a balingchamber adapted to receive tall grass biomass material and a compressionsystem adapted to compact the tall grass biomass material into aparallelepiped bale in the chamber, wherein the baling chamber comprisesa front wall consisting essentially of a reciprocating compressionplaten corresponding in dimensions to the width W and height H of thebale, opposing upper and lower walls corresponding in dimensions to thelength L and either of the W and H of the bale, and opposing sidewallscorresponding in dimensions to the L and the other of the W and H of thebale, and wherein the compression system is adjustable by conventionalcontrols to apply at least one operator-selectable compression platenpressure of between 22 psi and 30 psi to the tall grass biomass materialin the chamber.

For bale ejection through an open or reversibly opened back chamberwall, the compression system can apply a compression platen pressure ofat least (0.176×Pp×L)(H+W) pounds to move a bale of compacted tall grassbiomass material from the chamber, wherein Pp is the compression platenpressure expressed in pounds per square inch that the compression systemapplies to compact the bale in the chamber, and wherein L, H, and W areexpressed in inches

For bale ejection through a reversibly opened sidewall, the baler has anejection system adapted to apply a force of at least (Pp×W)(0.8H+0.176L)pounds to move a bale of compacted tall grass biomass material from thechamber through the opened sidewall, wherein Pp is the compressionplaten pressure expressed in pounds per square inch that the compressionsystem applies to compact the bale in the chamber, and wherein W, H, andL are expressed in inches.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a perspective view of a representative tall grass biomassbale;

FIG. 2 is a graph that contrasts the platen pressure curves of tallgrass biomass (at 60% wwb, 45% wwb, 30% wwb, 15% wwb, and dry weight)and timothy hay (at 15% wwb) when baled at optimum transportationdensities; and

FIG. 3 is a graph that contrasts the Poisson's ratio effects of tallgrass biomass (0.22), timothy hay (0.17), and woody biomass (0.11) whenbaled at optimum transportation densities.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The terms “parallelepiped” and “rectangular” are used interchangeablyherein to refer to a solid shape bounded by six substantially square orrectangular faces in which each pair of adjacent faces meets in asubstantially right angle.

The term “bale” as used herein refers to a parallelepiped-shaped bundleof compressed and bound biomass. FIG. 1 depicts a representative bale 10of compressed tall grass biomass 12 bound with a plurality of loops ofbinding material 14. Dimension W is perpendicular to the plane createdby the binding material that encircles the compressed biomass. DimensionH is perpendicular to W and in line with the binding material. DimensionL is perpendicular to the plane created by W and H. Binding material isparallel to L. Representative binding materials include wire,polypropylene twine, and banding straps. For stackability, balecompression is preferably along the L axis, most preferably with thebiomass material disposed substantially along the W axis, transectingthe binding material plane.

The term “green weight” as used herein refers to the weight of freshlyharvested tall grass biomass that has substantially the same moisturecontent, reportedly on the order of 44-66 percent wet-weight-basis (%wwb), as the stranding plants. The term “equilibrium weight” refers tothe eventual weight of tall grass biomass that has dried in bales underambient conditions to equilibrium moisture content. “Dry weight” as usedherein refers to the weight of tall grass biomass after drying toconstant weight at 221° F. (105° C.).

The “net energy content” of tall grass biomass bales is calculatedherein in terms of its dry weight organic component (disregarding watercontent) and with reference to a net energy value of 7,750 Btu per dryweight pound for switchgrass. (Fuel Value Calculator, USDA ForestProducts Laboratory, 2004.) For example, a 1,000-pound miscanthus baleat 45% water content is considered to have a net energy content of(((1-0.45)×1,000)×7,750) Btu.

The term “semi-trailer truck” as used herein refers to an articulatedrig consisting of a towing engine (“tractor”) coupled to a single“semi-trailer” (a trailer without a front axle), or to a “doubletrailer” consisting of a semi-trailer coupled to either anothersemi-trailer or a “full trailer” (a trailer supported by front and rearaxles), or to a ‘triple trailer” consisting of a semi-trailer coupled totwo full trailers. As used herein, the term “semi rig” refers to atractor & semi-trailer combination, commonly a 10-wheeled tractorcoupled to an 8-wheeled trailer; and the terms “double rig” and “triplerig” refer to tractors pulling two and three trailers, respectively. Thetrailers can be flatbed trailers, curtain siders, or box trailers. Theterm “fleet” refers to a group of semi-trailer trucks owned or operatedby a business or government agency.

The overall weight of a particular semi-trailer truck empty of cargo isreferred to herein as “curb weight.”

The term “cargo” as used herein refers to a plurality or multiplicity ofparallelepiped bales of tall grass biomass that are loaded for transporton or in the one or more trailers of a semi-trailer truck. The term“payload” refers to the weight, volume, and density characteristics ofthe cargo. The terms “payload weight” and “payload volume” refer to theweight and volume of the cargo, respectively.

The term “Gross Vehicle Weight (GVW)” as used herein refers to the totalweight of a semi-trailer truck and everything aboard, including cargo.The federal maximum GVW for semi-trailer trucks is 80,000 pounds. Doubleand triple rigs must additionally comply with the following federalbridge protection formula.

The term “Federal Bridge Gross Weight Formula” as used herein refers toFMCSA regulation §658, which is hereby incorporated by reference in itsentirety. This regulation limits the amount of weight that can be put oneach of a double or triple rig's axles, and how far apart the axles (orgroups of axles) must be to legally carry a given weight, expressed bythe formula:W=500((LN/N−1)+12N+36)wherein W is the overall gross weight on any group of two or moreconsecutive axles to the nearest 500 pounds, L is the distance in feetbetween the extreme of any group of two or more consecutive axles, and Nis the number of axles in the group under consideration.

As used herein the terms “maximum transport volume” and “maximumtransport weight” refer to the maximum volume and weight of cargo,respectively, that a particular semi-trailer truck can legallytransport. The maximum transport weight is determined by subtracting thecurb weight of the semi-trailer truck from the maximum allowable GVW ofthe truck. The term “optimal transport density” refers to the computeddensity (weight/volume) of a cargo that has both the maximum legaltransport volume and the maximum legal transport weight. Such anoptimized cargo is said to “cube out” the legal payload of asemi-trailer truck.

In ordinary circumstances, a tractor-coupled semi-trailer will weighabout 35,000 pounds, leaving about 45,000 pounds of payload capacity.The cargo space available on or in a semi-trailer is normally 48 or 53feet long and about 8 foot 4 inches wide and 8 foot 10 inches high.These general constraints give an optimal transport density range of12.7 to 11.5 lb/ft³. In practice, however, maximum transport weight andvolume limits depend specifically on a particular semi-trailer truck'scurb weight, trailer configuration, and travel route on federal andstate highways.

For example, the California Department of Transportation has relativelystrict regulations on weight and size limits for highway transportationvehicles. Semi-trailers are limited to 48 or 53 feet maximum length; andeach trailer in a double trailer cannot exceed 28 feet 6 inches inlength. For illustrative purposes, we describe an optimized bale sizeand density for cargo transport on a 48-foot semi-trailer in the stateof California. Considering payload volume, a 14-foot maximum allowableload height leaves 8 to 9 feet of useable cargo space. We assume an8-foot cargo height and an 8-foot loading width, leaving buffer spacesfor pallets, tarps, and straps. The exemplary volume, then, of cargothat can be transported on a semi-trailer in California (without specialpermits) is 48 ft×8 ft×8 ft equaling 3072 cubic feet.

With this information we can determine appropriate bale sizes for trucktransport of tall grass biomass on California highways. Table 1 listsseveral suitable bale configurations, sized for different businesses andtall grass biomass sources.

TABLE 1 Bale size 48 ft. trailer payload L × W × H L × W × H # Bale(inches) (bales) bales L/W ratio 24 × 16 × 24 24 × 16 × 4 576 1.5 48 ×32 × 32 12 × 3 × 3 108 1.5 64 × 48 × 32 9 × 2 × 3 54 2.0 96 × 48 × 48 6× 2 × 2 24 2.0

For example, 54 tall grass biomass bales sized 64×48×32 inches will cubeout the exemplary 3072 ft³ payload volume of a 48-ft semi trailer. Tomaximize packing efficiency, bale configurations are preferably selectedso that trailer dimensions are evenly divisible by bale dimensions. Inthis example the trailer length is divisible without remainder by thebale length dimension, and likewise trailer width by bale width, andtrailer height by bale height.

Tall grass biomass bales should preferably have an L/W and/or L/Hratio(s) of at least 1.5, as smaller ratios tend to produce egg-shapedbales rather than consistently stackable, rectangular bales. Mostpreferably, L/W and/or L/H ratio(s) of approximately 2 advantageouslypermit the bales to be stably interlocked on pallets or in stacks. Wenote that finished bale dimensions will increase by the amount ofstretch in the chosen binding material, e.g., polypropylene twinestretches under load more than steel wire. Consequently the balingchamber walls (discussed below) can be sized proportionately shorter(wherein w is the width of the compression platen, h is the height ofthe compression platen, and l is the length of the chamber), toaccommodate the anticipated stretch of particular binding materials.

Considering payload weight, a typical semi rig payload legal inCalifornia is 44,000 to 48,000 pounds. Combining these volume and weightconstraints gives an optimum transport density range of 14.3 to 15.6lb/ft³. Assuming a maximum payload weight of 45000 lbs, 54 biomass balessized 64×48×32 inches with an average green density of 14.6 lb/ft³ willcube out the truck. FIG. 2 indicates that green tall grass biomass (45%wwb) can be compressed to a density of about 14.6 lb/ft³ by a platenpressure force (i.e., baler system pressure applied to the platen timesthe area of the platen in inches) of about 4 psi. However, transportingsuch green biomass bales over long distances would be far from optimal,as this green payload would contain some ten tons of noncombustiblewater. Drying the bales prior to long-haul transport significantlyincreases the energy content of the biomass payload, but to predictablycube out the truck with dried biomass the green tall grass biomass mustbe baled at predetermined higher initial densities, for example as shownin Table 2.

TABLE 2 Bale at _% wwb Bale Size: ship at 64 × 48 × 32″ Baler 48 foottrailer payload _% wwb Vol Wt lbs/ Platen L × W × H # % % Btu ↓ (ft³)(lbs) ft³ Pressure (bales) bales lbs V W (×10⁶) 1a 45 57 833 14.6  ~4psi 9 × 2 × 3 54 45,000 86 100 191.8 45 1b 45 57 997 17.8 ~14 psi 9 × 2× 3 54 45,000 86 100 244.1 30 1c 45 57 1148 20.5 ~22 psi 9 × 2 × 3 5445,000 86 100 296.4 15 2a 30 57 833 14.6 ~16 psi 9 × 2 × 3 54 45,000 86100 244.1 30 2b 30 57 997 17.8 ~30 psi 9 × 2 × 3 54 45,000 86 100 296.415 3a 12.5 57 833 14.6 ~32 psi 9 × 2 × 3 54 45,000 86 100 305.2 12.5 3b12.5 57 713 12.5 ~20 psi 9 × 2 × 3 54 38,502 86 85 261.1 12.5 3c 12.5 57645 11.3 ~14 psi 9 × 2 × 3 54 45,000 86 77 236.2 12.5

In Table 2, row 1a summarizes the exemplary green bale cargo: fifty-four64×48×32 inch bales of green switchgrass at 45% wwb, compressed to about14.6 lb/ft³, will essentially cube out the maximum transport weightwhile filling about 86% of the available transport volume(3072/(48×8.3×9)). At an energy value of 7,750 Btu per dry weight pound,this green bale cargo has a net energy value of about 192 million Btu.

Row 1b indicates that green switchgrass (45% wwb) that is baled to about17.8 lb/ft³, at a platen pressure of about 14 psi, will dry down to themaximum payload weight at about 30% wwb. The resulting cargo has a netenergy content of about 244 million Btu.

Row 1c indicates that drying green bales down to 15% wwb increases thenet energy content of the cargo to about 296 million Btu, provided thegreen tall grass biomass is initially baled at a proportionally higherdensity (˜20.5 lb/ft³, at ˜22 psi) to accommodate the greater water lossduring dry down to the predetermined maximum payload weight.

Rows 2a and 2b present similar calculations for late season switchgrasswhen baled at 30% wwb. Row 3a presents a comparable optimized strategyfor baling and shipping switchgrass at 12.5% wwb. For comparison, rows3b and 3c show how net energy content decreases when switchgrass at12.5% wwb is baled at suboptimal platen pressures to lower densities.

In this manner, by selectively producing relatively dense tall grassbiomass bales for drying to predetermined optimum transport densities,especially by natural evaporation and transpiration under ambientconditions, the long-haul highway transportation and fuel costs per unitenergy delivered can be greatly reduced and optimized.

Additional economies can accrue during the baling process by limitingthe strength (weight) and power (weight, size, noise, and fuelconsumption) of the baler to achieve but not unnecessarily exceed anoptimized transport density range selected to accommodate particularbiomass types and trailer truck configurations.

The experimental data reported herein was acquired in a laboratory scalebaler constructed as disclosed in Example 1.

EXAMPLE 1 Laboratory Scale Baler Materials and Methods

Prior to designing and fabricating the bench-top lab baler, ourliterature review revealed insufficient prior data for the compression,expansion, and friction properties of compressed plant biomass typesneeded to optimally design a tall grass biomass baler. By using alab-scale baler rather than a full-scale machine, material and time weresaved in testing and validating hypotheses. The scaling was modeledafter the way forces and moments are scaled in homogeneous isotropicmaterials like steel and aluminum. Tall grass biomass under pressure canbe approximated as an isotropic solid. The pressure-pressurerelationships developed in the lab baler were incorporated as explainedin Example 2 into a full-scale prototype design.

The lab-scale combined baling and infeed chamber measured 68.8 cm (27inches) long, of which 49.5 cm (19.5 inches) was the enclosed balingchamber. The platen and end wall were 29.2×29.2 cm (11.5×11.5 inches).

The bulk of the lab baler structure was made from standard 1018 steel inthe forms of 50×50×6.4 mm wall (2×2×¼ inch) tubing and 50×50×6.4 mm(2×2×¼) angle. The volume of the bale chamber and infeed chamber wasencompassed by six sides. They consisted of three fixed sides, two sidesthat were part of the L shaped door, and the sixth side was formed bythe compression platen. The bottom and right side both extended from theretracted platen to the end wall. While the corners of these sides werewelded in place, the two rails of each side were formed by load beamsthat could sense force exerted perpendicular to the compression platen,either down or to the side. The opposite sides were formed by the doorwith the left side being full length, and the top being cut short todesignate the infeed. The door was hinged along the lower left cornerand clamped in two places opposite the hinge, one close to the infeedand one close to the end wall. The sides and ends of the chamber wereslotted such that binding twine could be pushed or pulled around thebale in six places, three in each plane perpendicular to the platenmotion. The platen and end wall each had nine evenly spaced posts tocreate the string passages around the ends of the completed bale.

Hydraulic fluid was moved by a Haldex Barnes Power Unit model number1400011, with a 1.5 kW (2 HP) motor capable of moving 95 cc per second(1.5 gpm) at up to 13.8 MPa (2000 psi). The compression cylinder wascontrolled by an open center, manual, monoblock valve. For safety, thevalve was positioned such that the operator could not have hands in theinfeed or baling chamber while operating the valve. Compression wasfacilitated by an 8.9 cm (3.5″) bore by 45.7 cm (18″) stroke 20.7 MPa(3000 psi) max cylinder. Maximum force was 85.6 kN (19250 pounds) andthe cylinder fully extended in 30 seconds (1.5 cm or 0.6 inches persecond). A pressure gauge and a pressure sensor were installed betweenthe directional valve and the base of the cylinder, thus allowing thecylinder pressure to be monitored even when the flow from the pumpstopped. A needle valve allowed a finely adjustable flow between thefront and rear of the cylinder, and a ball valve allowed oil to escapefrom the front of the cylinder back to the tank when the directioncontrol was in neutral. A second pressure gauge was located at the pumpso pressure could be measured when the control was in reverse.

A wheel type linear position sensor was used to record the position ofthe platen while hydraulic pressure (from which paten pressure wascalculated) and side force (from which Poisson's ratio effect wascalculated) were measured. Sensors outputs were recorded simultaneouslyat 15 times per second.

EXAMPLE 2 Engineering Constraints for Rectangular Tall Grass BiomassBalers

FIG. 2 discloses the range of compression platen pressures requisite tocompress tall grass biomass of various water contents to predeterminedtransport densities. This information can be used in two ways. The watercontent of winter killed tall grass biomass can be determined to selectan appropriate curve for correlating platen pressure with apredetermined optimum transport density. Alternatively, this informationcan be used to predict the weight loss resulting from drying green tallgrass biomass bales to lower water contents. In either case the biomassbaler's compression system can be routinely fabricated to target thecorresponding range of platen pressures requisite to achieve a desiredrange of transport densities.

In practice, expected bale densities are subject to some variabilitybut, by mounting a conventional load cell under the baling chamber, theweight of the tall grass biomass going into a bale can be monitoredduring loading and flake formation, and the platen pressure adjusted toachieve a completed bale of targeted density. Acceptable variations inbale density will tend to average out when the bales are loaded intomultiple-bale cargoes.

FIG. 3 discloses that tall grass biomass (switchgrass) exhibits aPoisson's ratio effect (PR) of approximately 22%. This physicalproperty, which is substantially independent of water content, isrequired to calculate the minimum mechanical strength of a balingchamber for producing tall grass biomass bales at the requisite platenpressures. The distributed force on the back wall is equal to the forceof the platen (P_(p)×A_(p)), but the force resisted (F_(w)) by the otherbaling chamber walls must be at least equal to:F _(w) =PR×P _(p) ×A _(w)wherein F_(w) is the distributed load against any one of the chamberwalls selected from among the upper wall, the lower wall, and either oneof the sidewalls of the rectangular baling chamber, P_(p) is the maximumpressure that the baler can apply by the compression platen, and A_(w)is the area of the selected wall. Substituting for the observedPoisson's ratio of compressed tall grass biomass, then:F _(w)≧0.22×P _(p) ×A _(w)wherein A_(w) is expressed in square inches.

In conventional practice, baler manufacturers will add standard factorsof safety to such calculated design constraints, as described in theliterature, e.g., Shigley 1963. SF is a predetermined design loadingmultiplier to ensure that the operational loading is not greater thanthe design loading. In a representative embodiment, such a calculatedupper limit for sidewall strength (0.22×P_(p)×A_(w)) may be multipliedby the same safety factor that the manufacturer chooses to use for thecompression platen, in which case SF as applied to the sidewalls iscalculated by dividing the predetermined design failure load of thecompression platen by the maximum pressure that the baler canoperationally apply by the compression platen (P_(p)), such that thedesign upper limit of the sidewalls is (0.22×P_(p)×A_(w)×SF).

Bale ejection requires that sufficient force be applied against the baleto overcome the total frictional forces (F_(f)) that the compressed tallgrass biomass applies to the chamber walls (typically steel) thatcontain it during ejection. We determined that the coefficient offriction of compressed tall grass tall grass biomass is approximately0.40 and decreases as the water content of the biomass decreases.Optionally, coating the baling chamber walls with a low frictionmaterial will reduce the applicable F_(f) value.

For ejection through an open or opened back chamber wall, the baleapplies frictional forces against the upper wall, the lower wall, andthe two sidewalls. For side ejection, the ejection system must overcomethe frictional forces against the platen, lower wall, back wall, andupper wall. Top or bottom ejection systems would be designed to overcomethe frictional forces against the platen, back wall, and sidewalls.

The frictional force that the bale applies against any one of thechamber walls is expressed as F_(f)=F_(n)×C_(f), where F_(n) is thenormal force (calculated below) and C_(f) is the coefficient of frictionof compressed tall grass biomass on the wall material.

Considering rear ejection, the pressure (P_(w)) that the compressed baleapplies against the upper, lower, and two sidewalls is equal to theplaten pressure times the Poisson's ratio, or P_(w)=P_(p)×PR.Alternatively, P_(w) can be expressed as the normal force divided by thearea of the wall, P_(w)=F_(n)/A_(w).

Assume that the area of the upper and lower walls is L×W; and that ofthe sidewalls is L×H. Then for each sidewall, P_(w)=F_(n)/(L×H), whichconverts to F_(n)=P_(w)×L×H. Substituting for P_(w), thenF_(n)=P_(p)×PR×L×H. Accordingly, for each sidewall:F _(f) =F _(n) ×C _(f)F _(f) =P _(p) ×PR×L×H×C _(f).Similarly, for the upper and lower walls:F _(f) =P _(p) ×PR×L×W×C _(f).In combination, then, the cumulative frictional forces during rearejection are:F _(f) total for rear ejection=2(P _(p) ×PR×L×H×C _(f))+2(P _(p)×PR×L×W×C _(f)).

Pursuant to this disclosure, for tall grass biomass the PR is 0.22 andC_(f) is 0.4. Thus, the rear ejection system should control thecompression platen to apply at least the following force (in pounds,when L, W, and H are expressed in inches) to eject the bale through theback wall of the baling chamber:F _(f) total for rear ejection=2(P _(p)×0.22×L×H×0.4)+2(P_(p)×0.22×L×W×0.4)(0.176×P _(p) ×L×H)+(0.176×P _(p) ×L×W)(0.176×P _(p)×L)(H+W).

For side ejection, the platen and back wall are compressed to the platenpressure, and so for these “sides” of the ejected bale:P _(p) =F _(n) /A _(p), or F _(n) =P _(p) ×W×H.However, the Poisson's ratio effect still applies to the F_(f) valuesfor the upper and lower walls, as calculated above. Thus, incombination:F _(f) total for side ejection=2(P _(p) ×W×H×C _(f))+2(P _(p) ×PR×L×W×C_(f))2(P _(p) ×W×H×0.4)+2(P _(p)×0.22×L×W×0.4)(0.8×P _(p) ×W×H)+(0.176×P_(p) ×L×W)(P _(p) ×W)(0.8H+0.176L).

Similarly, top or bottom ejection must overcome the frictional forcesagainst the platen, back wall, and sidewalls. Combining these forces inthe manner calculated above, the F_(f) total for top or bottom ejectionof a tall grass biomass bale compressed to optimum transport densityequals at least:F _(f)=2(P _(p) ×W×H×C _(f))+2(P _(p) ×PR×L×H×C _(f))2(P _(p)×W×H×0.4)+2(P _(p)×0.22×L×H×0.4)(0.8×P _(p) ×W×H)+(0.176×P _(p) ×L×H)(P_(p) ×H)(0.8W+0.176L).

Most preferably, the baler compression system is configured to compactthe tall grass biomass material with a platen pressure between about 22and 30 psi. This optimal range, for the most common case of delivery byhighway-legal trucks, encompasses the exemplary dry-down strategiesdisclosed in the Table 2 above. The baler compression system willtypically incorporate one or more hydraulic cylinders to advance theplaten and thereby compact the tall grass biomass material within thebaling chamber. The hydraulic system is preferably adjustable byconventional controls to encompass all or a substantial part of thisoptimal range, in order to permit the operator to select an appropriateplaten pressure to achieve a predetermined bale density, taking intoconsideration initial moisture content, expected dry-down period, andmode of transportation.

The invention accordingly permits an optimized tall grass biomasstransport system including a fleet of semi-trailer trucks that arereversibly loaded at transport intervals with cargoes of parallelepipedbales of tall grass biomass, wherein the aggregate weight of the loadedbales is at least 80% of the aggregate maximum cargo weight capacitiesof the loaded semi-trailer trucks, and wherein the aggregate volume ofthe bales is at least 80% of the aggregate maximum cargo volumecapacities of the loaded semi-trailer trucks. The trucks are preferablyloaded to at least 85%, and most preferably to at least 90%, of theirlegal payloads. To further reduce transportation costs, the tall grassbiomass bales should be dried before long-haul transport to averagemoisture contents of less than 30%, preferably less than 20%, and mostpreferably less than 15%.

In this manner, conventional semi-trailer trucks can be routinely loadedwith tall grass biomass payloads having net energy values of around 240million Btu or more, for economical transport over highway distances ofseveral hundred miles.

One of ordinary skill in the art will readily understand and appreciatethat the platen pressure v. bale density relationships disclosed in FIG.2 are just as useful, mutatis mutandis, to predictably and reproduciblyproduce bales of tall grass biomass at predetermined lowertransportation densities for short haul or barge transportation, as wellas at higher densities for long-haul transport by rail or ship. The costof hauling the extra air content of low-density bales by barge orshort-haul truck is relatively low, and that incremental cost may bemore than offset by lower fossil fuel consumption in the baling process.Trains and ships have more constrained payload volumes than barges, andmaximum higher payload weights than trucks, and so their cargoes can becubed out at maximum payload by baling at higher platen pressures, inthe substantially constant slope regions of the tall grass biomasscurves in FIG. 2. Moreover, FIG. 3 indicates that throughout the notedcompression ranges the observed Poisson's ratio of 0.22 applies.

CITATIONS

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While the preferred embodiment of the invention has been illustrated anddescribed, it will be appreciated that various changes can be madetherein without departing from the spirit and scope of the invention.

We claim:
 1. In a process of baling a biomass material in a balercomprising a chamber adapted to receive a biomass material and acompression system adapted to compact the biomass material into arectangular bale, the improvement comprising: compacting a switchgrassbiomass material at a compression pressure of between about 22 psi andabout 32 psi into a rectangular switchgrass bale having a bale densityof between 14.6 lb/ft³ and 20.5 lb/ft³.
 2. The process of claim 1wherein the rectangular switchgrass bale is 3×4×8 feet and weighsbetween 1,402 and 1,968 pounds.
 3. The process of claim 1 wherein theswitchgrass biomass material comprises whole stalks or billets.